Steel parts such as refrigerator racks which are subjected to corrosive conditions are commonly provided with protective coatings. Such coatings may include a zinc layer applied by electroplating, a chromate layer over the zinc, typically applied by immersing the zinc-coated part in a chromating solution and final coating with a synthetic resin.
The sequence of successive zinc, chromate, and resin coatings has been used commercially for various products including refrigerator racks. For example, this sequence is disclosed in U.S. Pat. Nos. 3,808,057 and 4,003,760. As there described, the chromate coating is applied by immersion of the zinc-plated part in a chromating solution. Other methods of application of chromate layers have been suggested, such as spraying, brushing, swabbing or electrolytic methods: Eppensteiner and Jenkins, "Chromate Conversion Coatings", Metal Finishing Guidebook and Directory 1990, pages 433-447, at page 433.
The application of protective coatings to steel refrigerator racks or similar parts is believed to have been carried out by interrupting the coating procedure after the zinc electroplating. At a later time and in a separate production line, the zinc-coated parts have been subjected to chromating and thereafter to resin coating. As far as it is known, no continuous production method has been developed in which a steel part, such as a refrigerator rack, can be sequentially processed without interruption to apply successive zinc, chromate, and synthetic resin coatings.